impact of upper nile projects on the hydraulic performance...

Twentieth International Water Technology Conference, IWTC20 Hurghada, 18-20 May 2017

549

IMPACT OF UPPER NILE PROJECTS ON THE HYDRAULIC

PERFORMANCE OF THE WHITE NILE AND JEBEL AULIA DAM

OPERATION

A.S. ZAGHLOUL1, M. ELSAYED

2, A. EL ZAWAHRY

3

1 Associate Prof., Irrigation and Hydraulics Department, Faculty of Engineering, Cairo University,

Giza, Egypt, E-mail: [email protected] 2 Chairman, High Dam authority, MWRI, Egypt, E-mail: [email protected]

3 Professor, Irrigation and Hydraulics Department, Faculty of Engineering, Cairo University, Giza,

Egypt, E-mail: [email protected]

ABSTRACT

To increase the Nile flow and to secure water requirements for the Egyptian population, one of

the options is to implement Upper Nile Projects. Studies showed that these projects may secure about

9 BCM per year for Egypt after implementation (estimated at Aswan). There are three mega projects

in the upper Nile reach to increase the yield of River Nile through saving the lost water in the swampy

area in sudd region in south Sudan. Yield of these projects will flow into the White Nile which is

already suffering from overflow in some reaches due to its limited flow capacity. Also increasing the

discharges and levels in the White Nile may have a negative effect on Jebel Aulia Dam and cause

hazardous overtopping.

The objective is to assess the White Nile hydraulic capacity to accommodate the additional

expected discharges from the upper Nile projects and simulate the locations of expected floods. Also,

the gate operation of Jebel Aulia dam is studied and the necessary modifications of its operation rules

to accommodate the new White Nile increased flow are recommended.

HEC-RAS Program is used to estimate the water levels in the cross sections at different points

along the White Nile. Water budget or water balance method is used for estimating water losses in the

study area. Frequency analysis and water budget were done using Mat lab program. River flow

simulation is presented for eight scenarios of Upper Nile project implementation. Points along the

study reach which need bank rising are presented and the minimum gate opening at Jebel Aulia dam

are calculated and recommended. Results can be applied for floodplain management and flood

protection in the study area and useful in operation of Jebel Aulia dam.

Keywords: White Nile, Capacity, Upper Nile Projects

1 THE STUDY REACH

As shown in “Fig. 1”, The study reach extends 767 km, it starts from Malakal station in the south

at km on the White Nile, measured from Khartoum, and extends to Jebel Aulia Dam in the north at

km 44, (NWS, 2000). The average bed slope for the study reach is about 1.7 cm/ km. HEC-RAS

Software is dependent on geometric, hydraulic, and hydrologic data. Geometric data consists of cross-

sectional geometry along the study reach and available in literature, (NWS, 2000) and (Samah 1974).

Data of 50 cross-sections done by the Egyptian engineering missions in Sudan (Mission, 1961 &

Mission 1970) are used in the analysis. Sections are surveyed from the top of the left bank to the top

of right bank. Monthly data of discharges measured at Malakal station from 1907 to 1997 is used

(MWRI, 2000). Gauge stations in the White Nile are located in Getein, Wad El-Zaki, El-Shawal,

Rabak, Gebalien, Renk, Melut, and Makakal. Discharge Stations are located in Malakal, Melut and

Mogern (D.S. Jebel Aulia dam). Jebel Aulia Dam was constructed in 1937 on the White Nile (about

40 km south of Khartoum).


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Figure 1. Location map of the study reach of the White Nile under consideration

Jebel Aulia Dam was built in 1937 on the White Nile, about 44 km south of Khartoum to provide

a maximum of 3.6 BCM storage water. Due to the gentle slope of the White Nile, the upstream lake of

Jebel Aulia dam extends about 628 km upstream the dam in case of maximum storage level (377.40).

The back water curve of the dam ends just upstream Melut station. The dam has a sixty sluice vents,

of which the ten western vents were not fitted with gates, being blocked with heavy R.C diaphragms.

Three training walls were constructed downstream of the sluice-dam, dividing the fifty sluice gates

into three groups, ten, twenty and twenty respectively. Each gate is 4.5 m high and 3 m wide. The

lowest downstream level is 370.75 meters. Downstream of the dam, the river is about 600 m in width;

its greatest depth is 15 feet, the average discharge ranges from 500 m3/s in April to about 1,300 m3/s

in November (Mission, 1970 & MWRI, 1936).

2 UPPER NILE PROJECTS

There are three mega projects in upper Nile reach to increase the yield of River Nile by saving the

lost water in the swampy area in sudd region in south Sudan. “Fig. 2” is a location map of these

projects (NWS 2009). Table 1 shows the expected water benefit from each Projects (PJTC,1961 &

Afifi, 1995).

Figure 2. Location of the Upper Nile Projects


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Table 1. Expected water benefit from upper Nile projects (PJTC, 1961 & Afifi, 1995)

No. Project Water Benefit from Upper Nile Projects (Million.m3/

day)

1 Jonglei Canal (Phase I&

II)

43

2 Machar Marshes 25

3 Bahr El-Ghazal Canals 21

Total 89

3 DATA AND DESIGN DISCHARGES

Malakal discharge station was established in 1907 on the right bank of the White Nile. It is far

about 146 km from Lake No and about 2652 km from Aswan. The discharge at the station is

measured usually three times per week while the staff gauge is read every day. The maximum

discharge which was measured at Malakal station is 211.7 M. m3/day, while the minimum discharge is

27.6 M. m3 /day for the period (1907-1997), (El-Sayed, 2013). Malakal design discharge which will

be applied in Hec-Ras Model is calculated as the summation of Malakal normal monthly discharge

and the expected flow rates of Upper Nile Projects.

3.1 Malakal Station Design Discharge.

Frequency analysis of flow data at Malakal is done using Matlab program. Extreme values of

normal monthly discharges are estimated based on the available data from 1907 to 1997 for return

periods (10, 25, 50, and 100) years. Extreme values for max daily discharges at Malakal are calculated

as the average obtained by MatLab, applying four methods (log Pearson III- log normal- normal-

Pearson III). For example, the resulting design discharge for 100 years return period is Qmalakal =

(164.7895+166.1694+192.6401+191.7669)/4=178.8 M. m3/ day which is equivalent to 2069 m3/ sec.

Thus, Malakal design discharge which will be applied in Hec-Ras Model is equal to the

summation of Malakal normal monthly discharge and the expected flow rates of Upper Nile Projects.

Therefore, Max design discharge = Q Normal + Q Upper Nile Projects = 178.8+ 89 = 267.8 M.m3/

day, =3100 m3/ sec. The discharge which will be used in HEC RAS model is Malakal design

discharge at the first upstream section (RS=100) and will decrease according to the distance between

sections by the rate of losses until US Jebel Aulia Dam section (RS=51).

3.2 Water Losses from Malakal Station to Jebel Aulia Dam

El-Sayed (2013) considered the actual data of water losses in the different parts of the reach

(NWS 2000) for estimating the water losses in the study reach. Water losses and water abstraction for

irrigation purpose in the reach between Malakal and Jebel Aulia Dam is assumed to accrue uniformly

along the Nile reach and subtracted from Malakal design discharge in order to estimate the design

flow rates for all the cross sections.

In this study the losses considered losses are 3.15 BCM/year for the losses and 1.500 BCM/year

for water abstraction for irrigation purpose. This makes a maximum total of 4.65 BCM/ year,

equivalent to 0.1902 m3/ sec /km. In the absence of daily losses data, the ratio between the extreme

value of Malakal discharge based on max daily discharge and the extreme value Malakal discharge

based on monthly discharge are used in estimating the extreme value of daily. El-Sayed (2013)

generated these factors for the different return periods as 1.7, 1017, 1013, and 1.09 for the return

periods 10, 25, 50, and 100 years respectively


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4 MODEL CALIBRATION

The HEC-RAS model is calibrated against the Manning’s roughness coefficient (n-value) using

the flow hydrograph passed through Malakal station at the section RS= 100 during the year (2000-

2001). Calibration began with an estimate of n equal (0.018-0.03) for the main channel and (0.022-

0.04) for the flood plains as recommended by (Eizel, 2010). Taking the boundary condition is the

stage hydrograph upstream Jebel Aulia Dam and flow hydrograph at Malakal station RS= 100,

(2000-2001) and running unsteady flow. Trial and error iterations are done until matching with the

measured stage hydrograph for Rabek station section RS= 70 (km 492 from Malakal). “Table 2”

shows the different n–values used.

Table 2. The different values for Roughness Coefficient n

(n-value) n1 n2 n3 n4

Main Channel 0.03 0.025 0.02 0.018

Floodplain 0.04 0.03 0.025 0.022

A comparison between the measures and simulated hydrographs, for different n values, at Rabek

station section RS=70 are plotted in “Fig. 3”. It shows that the hydrograph of n2 well matches the

observed one. Figures 4 and 5 Show the water surface levels at Malakal (River Station) RS= 100 and

upstream Jebel Aulia Dam (RS =51) for the flow hydrograph of Malakal 2000-2001.

Figure 3. Simulated and measured stage hydrographs for Rabek station at RS=70 for different n values

374.60374.80375.00375.20375.40375.60375.80376.00376.20376.40376.60376.80377.00377.20377.40377.60377.80378.00

01/0

1/…

11/0

1/…

21/0

1/…

31/0

1/…

10/0

2/…

20/0

2/…

01/0

3/…

11/0

3/…

21/0

3/…

31/0

3/…

10/0

4/…

20/0

4/…

30/0

4/…

10/0

5/…

20/0

5/…

30/0

5/…

09/0

6/…

19/0

6/…

29/0

6/…

09/0

7/…

19/0

7/…

29/0

7/…

08/0

8/…

18/0

8/…

28/0

8/…

07/0

9/…

17/0

9/…

27/0

9/…

Measured n1 n2 n3 n4

Date

Measured and Obseved level for Rabek Station km 492 from Malakal Station ( 2000-2001)

Leve

l m


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Figure 4. Cross section (RS=100) of White Nile at Malakal

Figure 5. Cross section (RS=51) of the White Nile upstream Jebel Aulia Dam km (767) from Malakal

5 MODEL VALIDATION

For assessment of the model's ability to accurately reproduce known results, The developed Hec-

Ras model was run at the high flow rate. The computed water surface profile is compared to the

measured profile. Actual data of the White Nile flow hydrograph for Malakal Station (2007-2008) at

upstream with a boundary condition stage and flow hydrograph upstream of Jebel Aulia Dam are

used. The calibrated n-value 0.025 for the main channel and 0.03 for the flood plains are used. The

stage hydrograph is calculated for Renk station RS=80, located at km 326 from Malakal. “Fig. 6”

shows that the simulated stage hydrograph well matches the observed one.


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Figure 6. The stage hydrographs at Renk Station RS=80, located at km 326 from Malakal Station

6 RESULTS OF MODEL APPLICATION AND DISCUSSIONS

The developed Hec-Ras model is used for simulating the water surface profiles for the channel

reach under consideration for different flow scenarios under steady state conditions. The simulation

results are further used for estimating the locations of expected overflow regions which need

protection works and raising the banks. Also, the resulting simulation water levels upstream of the

dam are further used to find the minimum gate openings of the dam to avoid overtopping.

6.1 Simulation of Current Situation for White Nile (Malkal- Jebel Aulia Dam).

The current condition flow condition is simulated for the study reach to know the current

problems. The design discharge in this case study will be only the extreme values for daily discharge

at Malakal station and the corresponding losses and abstraction without any upper Nile projects

contribution, for different return period (10,25,50,100 years). Thus: Q design at Malakal are taken 2069,

1944, 1805 and 1642 m3/sec respectively, and the boundary conditions of the Hec-Ras model, is the

water level upstream the Dam's gate (377.40). The water profile “Fig. 7” and floodplain for different

cross sections in the study reach along 767 km from Malakal to Jebel Aulia Dam are obtained. Also

“Fig. 8” shows cross section NO: 95 at 113.75 km from Malakal and the occurring overflow and the

different water level for different return periods. “Table 3” shows the different overflow lengths in

Left and right banks for Base Line conditions for Q100 years. From the table it can be concluded that

the White Nile already have overflow problems in about 154.9 km of its length.

Table 3. The different overflow lengths for the current flow conditions (Base Line)

Sec No: 95 94 93 78 77 70 64 58 57 56

Total km

From

Malakal

103.04 122.55 142.08 372.7 392.59 492.24 578.49 680.14 693.14 704.14

Left

Bank m 0 19523 19210 0 9800 7900 0 13000 11000 19100 99500

Right

Bank

m

19508 0 0 19890 0 0 16000 0 0 0 55400


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Figure 7. Longitudinal Water surface profile along the White Nile between Malakal and Jebel Aulia Dam

(Base Line Situation)

Figure 8. Cross section at RS= 95 , located 103.44 km from Malakal (Base Line Situation)

6.2 Flow Simulation for Different Implementation Scenarios

Table 4 shows the different scenarios of implementation of the Upper Nile projects mentioned in

“Table 1” and the Baseline Situation. The downstream boundary condition is the water levels

upstream the dam's gate (377.40). For each scenario, Hec-Ras was run to simulate the flow along the

river reach considered. Only results of scenario (1) will be presented as it represents the worst flow

conditions.

Table 4. Flow in the different scenarios and the Baseline Situation used for simulation

Scenarios NO: Details of projects Q 100 years m

3/sec

(Malakal)

1 Q Malakal+ Q Ghazal +Q Machar +Q Jonglie 3100

2 Q Malakal+ Q Jongli 2567

3 Q Malakal+ Q Machar 2358

4 Q Malakal+ Q Ghazal 2312

5 Q Malakal+ Q Jongli+Q Machar 2856

6 Q Malakal+ Q Jongli+Q Ghazal 2810

7 Q Malakal+ Q Ghazal+Q Machar 2601

8 Q Malakal Base Line Situation ( current conditions) 2069


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“Fig. 9” shows the longitudinal water profile in scenario (1), along 767 km from Malakal to Jebel

Aulia Dam for different return periods. “Fig. 10” shows section RS= 95 and different water surface

level for different period and different discharges and over flow as example and typical cross section.

“Table 5” shows the lengths of expected overflow regions in Left and right banks in scenario (1) for

100 years return period. From “Table 5” and “Fig. 10” it can be concluded that the length of overflow

regions will increase to a total of 439 km. “Table 6” summarizes the results obtained for all the

different scenarios and base line situation. It is clear that the White Nile has already overflow

problems in different sections. From “Table 3” and Table(5), it can be noticed that most of overflow

sections are in upper downstream portion of study reach as shown in “Fig. 11”

Figure 9. Longitudinal water surface profile along the White Nile between Malakal and Jebel Aulia dam

for Scenario (1)

Figure 10. Cross section RS= 95, located 103.44 km from Malakal for Scenario (1)

Table 5. The different overflow lengths in Left and right banks for Scenario (1)

NO km From Malakal River Station Left Bank m Right Bank m

1 0 100 0 20750

2 20.750 99 18889 0

3 63.519 97 0 19845

4 83.364 96 19680 0

5 103.044 95 0 19508

6 122.552 94 19523 0


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NO km From Malakal River Station Left Bank m Right Bank m

7 142.075 93 19210 0

8 191.485 89 0 15660

9 287.325 82 26995 0

10 372.698 78 0 19890

11 392.588 77 9800 0

12 411.888 75 20858 0

13 432.746 74 15990 0

14 448.736 73 0 5550

15 477.536 71 14700 0

16 492.236 70 7900 0

17 578.486 64 16000 16000

18 634.186 61 18950 0

19 653.136 60 13000 0

20 680.136 58 13000 0

21 693.136 57 11000 1100

22 704.136 56 19100 0

23 734.136 54 15000 0

25 749.136 53 15000 0

26 764.136 52 13100 13000

Total Length

308000 131000

6.3 Safety of Jebel -Aulia Dam Against Overtopping

To determine the minimum gate opening to avoid dam overtopping, the well known gate

discharge equation is used as;

(1)

Where Number of Gates =50 Gate, Q is the gates discharge, A is the area of the gate, y is the

upstream water depth = (dam crest level- upstream bed level) = 379-368=11 m, ytail is the normal

downstream water depth, and Cd is calibrated coefficient for dam gate = 0.66

Manning equation is used to calculate the normal ytail. The roughness coefficient is taken 0.04

downstream of dam where the flow is shallow and cross section bed width is taken 2000 m. The

resulting ytail is 4.5 m. Considering the crest level 379 and the discharge at the dam, the critical

minimum gate opening, required to prevent overtopping is calculated using Equation 1.

Outputs of the Hec-Ras model obtained for the 8 scenarios mentioned in “Table 4” provided the

water level and discharge upstream the dam gates. Corresponding maximum water levels and depths

are calculated downstream of dam gates. These levels are used in equation (1) to obtain the minimum

gate opening to pass the discharge of each scenario. “Table 7” shows the Minimum Gate Opening at

maximum and minimum downstream water levels of Jebel Aulia Dam for the different 7 scenarios

and for the current condition for Q100 years. It shows that the 50 gates of Jebel Aulia Dam are

enough to pass the maximum discharges after implementing the upper Nile projects subject to the

condition of opening the control gates more than the minimum shown values. For each gate opening,

back water curve extend upstream of the dam as simulated in “Fig. 11”.

Table 6. The different overflow lengths for All Scenarios and Base Line Situation for Q100 years.

)(**2** taild yygAcQ


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Scenarios

NO: Details of projects

Q 100 years

m3/sec Malakal

Left

Bank

km

Right

Bank km

Total

Length

km

1

Q Malakal+Q

Ghaza+Q Machar+Q

Jongli 3100 308.0 131.0 439.0

2 Q Malakal+Q Jongli 2567 233.0 61.0 294.0

3 Q Malakal+Q Machar 2358 198.0 61.0 259.0

4 Q Malakal+Q Ghazal 2312 182.0 61.0 243.0

5

Q Malakal+Q

Jongli+Q Machar 2856 284.0 97.0 381.0

6

Q Malakal+Q

Jongli+Q Ghazal 2810 284.0 82.0 366.0

7

Q Malakal+Q

Ghaza+Q Machar 2601 260.0 82.0 342.0

8

Base Line Situation

(current condition) 2069 99.5 55.4 154.9

Table 7. The Minimum Gate Opening for the two cases of max and min downstream water level

Scenarios

NO: Details of Projects

Q

Malakal

100 years

m3/sec

Min Gate

Opening

(m)

H .L.D S

Min Gate

Opening

( m )

L .L.D S

1 Q Malakal+Q Ghaza+Q Machar+Q

Jongli 3100 4.09 2.44

2 Q Malakal+Q Jongli 2567 3.47 2.05

3 Q Malakal+Q Machar 2358 3.11 1.87

4 Q Malakal+Q Ghazal 2312 3.06 1.83

5 Q Malakal+Q Jongli+Q Machar 2856 3.82 2.27

6 Q Malakal+Q Jongli+Q Ghazal 2810 3.78 2.20

7 Q Malakal+Q Ghaza+Q Machar 2601 3.65 2.07

8 Base Line Situation 2069 2.76 1.70

H.L.D.S high water level at downstream.

L.L.D.S low water level at downstream.


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Figure 11. Water surface profile along the White Nile between Malakal and Jebel Aulia Dam For two

cases of Gates Opening

7 CONCLUSIONS

In this study, actual historical flow data of the White Nile reach from Malakal to Jebel- Aulia dam

are used in Hec-Ras model for simulating the hydraulic performance. The study has identified the

locations along the White Nile that face flooding for 7 scenarios and current condition. Results has

shown flood protection is required at the specified areas for each scenario. Even the current conditions

suffer from floods in 55.0 km and 155 km from the left and the right banks respectively. Therefore it

needs urgent protection at the specified locations. With the implementation of the upper-Nile projects,

about 308.0 km and 131.0 km from the left and the right banks will overflow and need protection.

The minimum gate openings of Jebel Aulia Dam to avoid dam overtopping are estimated for 7

scenarios. When the downstream water level is minimum, the minimum gate opening to pass the max

discharges is 2.44 m for the 50 gates. When the downstream water level is maximum, the minimum

gate opening is 4.10 m. Respecting the recommended minimum gate openings, the 50 gates of Jebel

Aulia Dam are enough to pass the max discharges for all upper Nile Projects and no needs to use the

spare gates. The protection levees works recommended along the White Nile banks should be

implemented in parallel with the Upper Nile projects implementation

REFERENCES

Afifi, A. K & Ezzat, M. N (1995) Nile Control and Conservation Projects, Nile Water Sector

report, MWRI, Egypt

Eizel-Din, M.A. & Saghayroon, E.(2010) Trap Efficiency of Reservoirs on the Nile River, a

technical report, Ministry of Irrigation, Khartoum, Sudan

El-Sayed, M. (2013) Impact of proposed upper Nile projects on the hydraulic performance of

the white Nile and jebel aulia dam operation rules”, MSc. Thesis, Irrigation and Hydraulics

Department, Faculty of Engineering, Cairo University, 2013

Mission E. I (1961) Estimating the Areas and Contains of Gable- Aulia Reservoir, Technical

report by the Egyptian irrigation mission in Sudan, MWRI, Egypt


560

Mission E. I (1970) Jebel Aulia annual report, Technical report by the Egyptian irrigation

mission in Sudan, MWRI, Egypt, 1970-1971

MWRI (2000) The National Water Resources Plan 2017, technical report by Planning sector,

MWRI, Egypt

MWRI (1936) The Working Arrangement for Operating the Jebel Aulia Dam with Notes

Revised, Technical report, Egypt

NWS (2000) Nile Basin Encyclopaedia 1912-2000, Nile Water Sector, MWRI, Egypt

PJTC (1961) First Annual Report 1960/1961, Permanent Technical Joint Commission for Nile

Water, Sudan

Samah, A. H. (1974) Notes about the White Nile Efficiency “From Lake No to the Mouth of

the White Nile“, MWRI report, Egypt

impact of upper nile projects on the hydraulic performance...

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